Yesterday, 04 supercharged stang loss of power, and started knocking loudly, where do i start to find the issue? no computer codes are thrown. Also, plug electrode is burned off #1 plug.

thanks,

tim

 

A piston engine needs three basic things to run: 1) a combustible mix of fuel and air, 2) the ability to compress that mixture, 3) the ability to ignite the compressed mixture.

For a modern EFI engine, of the three, number 2) is purely mechanical--do a compression test; start with the #1 hole. The missing electrode sounds like explosive detonation...

 

You might have blown a hole in your piston.... Compression test cylinder 1.

 

ran compression on all cylinders, they seem to be all over the place, can't get a consistent reading.... from 45 to 90 pounds... don't know much about the motor, was built when i got it.... looks like real low compression, any suggestions.

 

You will have to yank the heads and "see what you can see". If you get lucky it's top end problems, however it sounds as though explosive detonation went through the engine like a reaping machine...

 

45-90 PSI seems VERY low. Even on a low compression motor. Time to pull the heads.

 

+1, that would be low on a lawn mower.

The low-end service limit for the 4.6L 2V is 135psi, a good engine should be 150psi or better. The lowest should be no less than 75% of the highest, and if one or more actually read that low you're getting close to rebuild time.

Last time I checked mine (at 80k miles or so) I got 175-185, dry--surprised the heck out of me and almost blew the tester out of my hand, I switched over to the screw-in adapter after that...

 

not trying to offend you, but is there a chance that you maybe didnt run the compression check right? Sounds like you had a major problem in one of the cylinders.... so under 100psi for the rest makes me wonder if you ran the compression check right. Because that would mean you fried the whole motor not just part of it. make sure your getting a good seal and that your turning the engine over i believe its 4 times to get the pressure to build correctally. and if you still have low numbers, add a teaspoon? cant remember how much, of oil into a cylinder and see if the pressure improves, if so your fried the rings, which would be my guess if they are all low. Doesnt sound like you blew a hole in a piston tho, which is good news....sort of.

 

i had 160-165 on mine around 110k before i spun the bearings again. CLIFF!!! i need your help in my tranny question post!! sorry for the thread jack. :?)

 

it is odd, the car will start and run pretty smooth, just has a knock and not much power... could just be a bad tester, it's a loaner i picked up from autozone for a bit.... there was several fittings on the compression tester I've used it with and without the adapters, the compression just seems to be all over the place with no consistency. hate to tear into the motor if only the heads need to come off... i'll go pick up another tester, they're pretty basic to use, i pulled all the plugs out and have been going back and forth through all the cylinders several times trying to get a consistent reading. appreciate all the advice.